1. Field of Invention
The present invention relates to a novel self-contained imaging sheet which carries (1) a layer of microcapsules containing a photosensitive composition and an image forming agent and (2) a developer material on the surface of a support. More particularly, it relates to a self-contained imaging sheet wherein the layer of microcapsules is present as a first layer on one surface of the support and the developer material is present as a second layer contiguous with the first layer of microcapsules, and to a process for reproducing images on plain paper using the novel self-contained imaging sheet.
2. Prior Art
U.S. Pat. No. 4,399,209 to The Mead Corporation describes a transfer imaging system wherein an imaging sheet comprising a support and a layer of microcapsules containing a chromogenic material and a photosensitive composition is imagewise exposed to actinic radiation. The exposed sheet is assembled with a developer sheet and the two are passed through a calendar nip whereupon the microcapsules rupture and the contents of the microcapsules are image-wise transferred to the developer sheet where they react and form a colored image.
Typically, the photosensitive composition is a photocurable composition containing an ethylenically unsaturated compound and a photoinitiator. The Chromogenic material is a substantially colorless electron-donating color former, and the developer is an electron-acceptor such as an aromatic carboxylic acid salt which is capable of reacting with the color former and forming a visible dye image. Upon image-wise exposing the imaging sheet to actinic radiation, the internal phase of the microcapsules is hardened in the exposed areas. The internal phase remains liquid in the unexposed areas and may be hardened to an intermediate degree in areas receiving an intermediate level of exposure. Thus, the microcapsules in the unexposed areas are capable of rupturing and releasing the internal phase upon subjecting the exposed imaging sheet to a uniform rupturing force. The microcapsules in the underexposed areas may rupture and release the internal phase to an intermediate degree, however, in the exposed areas, the hardened photosensitive composition prevents the microcapsules from releasing the internal phase. In this manner, the internal phase of the microcapsules is image-wise released and transferred to the developer sheet where the image is formed.
While the transfer imaging system described in U.S. Pat. No. 4,399,209 can be used in numerous formats and applications, the user usually must purchase two coated paper products to reproduce images; namely, the imaging sheet and the developer sheet. This has several disadvantages. If the imaging sheet and the developer sheet are not designed to be used together, image quality may not be up to standard. More importantly, the developer sheet does not have the appearance, tactility, and other physical properties found in office bond paper.
U.S. Pat. No. 4,701,397 to The Mead Corporation relates to a process for forming images on plain paper by image area-wise transfer of a self-contained coating comprising a developer-containing resin and a microencapsulated photosensitive composition containing a color former. The developer-containing resin is provided on an imaging sheet in the same layer as a microencapsulated photosensitive composition or it may be provided as a separate contiguous layer. Images are formed by image-wise exposing the imaging sheet to actinic radiation, assembling the imaging sheet with a sheet of plain paper, heating the assembly, and subjecting the assembly to a uniform rupturing and transfer force. Upon heating and application of the rupture and transfer force, the microcapsules image-wise release the internal phase, the color former reacts with the developer and the image areas become adhered to the plain paper's surface. Upon separating the imaging sheet from the plain paper, the image areas are selectively transferred to the plain paper while the non-image areas remain adhered to the imaging sheet. both color former and developer-containing resin are transferred, as a unit, to the paper sheet.
U.S. Pat. No. 4,751,165 to The Mead Corporation is a continuation-in-part of the above-mentioned U.S. Pat. No. 4,701,397 and relates to the imaging sheet described in the parent case.
U.S. Pat. No. 4,865,938 to Brother relates to photo and pressure recording media which may consist of a self-contained imaging sheet wherein an adhesive member is added to the configuration of the imaging sheet. No consideration is given to placing the developer resin on top of the capsule layers and using modifications of this layer to produce a pressure activated adhesive.
U.S. Pat. No. 4,766,050 to The Mead Corporation relates to a photosensitive material having a support, an opacifying layer, a layer containing microcapsules and a layer of developer material. The layers are positioned such that upon rupturing the microcapsules, the color former diffuses to the developer layer to form an image therein. The final image is viewed against the opacifying agent which provides a white background.
U.S. Pat. Nos. 4,440,846; 4,508,807 and 4,622,282 and U.K. Pat. Appln. 2 202 641 A all disclose self-contained imaging sheets wherein the developer resin and photosensitive microcapsules are in the same layer or the developer resin is contained between the support and the microcapsule layer.
The inefficient configuration of the layers on the imaging sheet and, more importantly, the need for application of heat to induce adhesion to the paper in the above prior art cause poor image discrimination and clarity. Furthermore, capsule fragments of ruptured microcapsules are inadvertently transferred to the new base together with the developer resin. This is particularly undesirable when preparing OHP transparencies because of haze introduced by light scattering caused by broken and possibly unbroken capsules. Another problem occurs when capsules contain colored species such as dyes, pigments or colored photoinitiators. These capsules must not be transferred because the coloration will interfere with Dmin and other low color density areas in the final print.